1. Field of the Invention
The present invention relates to a RF amplifier, and more particularly to an IDSS (saturated drain to source current) RF amplifier adapted to a communication system.
2. Description of the Related Art
Traditional military RF frequency amplifiers are made by thin film technology. This expensive technology makes RF amplifiers become high cost components. Because of the mass-production requirement, most RE amplifiers of the modem communication systems are manufactured on printed circuit boards to reduce costs. The penalty is an oscillation resulted from the parasitic effect of bias circuits. There are two ways widely used to supply a DC power in designing a RF amplifier, a dual-bias circuit and a self-bias circuit The former makes the design of RF amplifier complex, and the later enhances oscillation easily.
To improve the gain and sensitivity, usually the RF amplifier is used as a low noise amplifier (LNA) which determines the noise figure of the whole receiver. The LNA is the most essential and important component in a receiver system.
To achieve a larger gain, in general, the RF amplifier includes two stages of amplifiers. It causes more power consumption and system instability. To design a RF amplifier with a simple bias circuit with a high stability, it is a quite big challenge for microwave engineers.
Accordingly, the prior art amplifier of the communication system has following disadvantages:
1. Because of the parasitic effect of a resistor and a capacitor of the bias circuit, noises and oscillation are easily generated in a self-bias amplifier of the receiver.
2. The prior art amplifier usually uses the dual-bias which requires a DC to DC converter to generate negative supply bias.